Electron beam freeform fabrication (EBF3) is a manufacturing deposition process in which an electron beam is used in conjunction with a wire feed to progressively deposit material onto a substrate in a layered manner. The electron beam is translated with respect to a surface of the substrate while the wire is melted and fed into a molten pool. In an EBF3 process, a design drawing of a three-dimensional (3D) object can be sliced into different layers as a preparatory step, with the electron been tracing each of the various layers within a vacuum chamber. The layers ultimately cool into a desired complex or 3D shape.
Taminger U.S. Patent Publication No. 2010/0260410 discloses a closed-loop control method and apparatus for an electron beam freeform fabrication (EBF3) process. The method of the '410 application can include use of one or more algorithms that are executed via a host machine of the apparatus set forth in the Taminger '410 application. The method uses a sensor or sensors to automatically detect or measure features of interest in the EBF3 process, e.g., by imaging molten pool during the EBF3 process. Detecting/measuring can be accomplished utilizing cameras, thermal sensors, and/or other suitable means. Sensor data describing the features of interest is fed into the host machine, which evaluates the sensor data to detect a magnitude/degree and/or a rate of change in the features of interest. The algorithm generates a feedback signal which is used by the host machine to modify a set of input parameters to the EBF3 process.
The Taminger '410 application discloses a closed-loop control method for an EBF3 process wherein a wire is melted and progressively deposited in layers onto a suitable substrate to form a complex product. The method includes detecting or measuring a feature of interest of the molten pool during the EBF3 process using at least one sensor, continuously evaluating the feature of interest to determine, in real time, a change occurring therein, and automatically modifying a set of input parameters to the EBF3 process to thereby control the EBF3 process.
The Taminger '410 patent publication also discloses an apparatus that provides closed-loop control of the EBF3 process, with the apparatus including an electron gun adapted for generating an electron beam, and a wire feeder for feeding a wire toward a substrate where the wire, once melted into a molten pool by the beam, is progressively deposited into layers onto the substrate. The apparatus also includes a host machine and at least one sensor. The sensors are adapted for detecting or measuring a feature of interest of a molten pool formed during the EBF3 process, and the host machine executes one or more algorithms to continuously evaluate the feature of interest and determine, in real time, a change occurring therein. The host machine automatically modifies a set of input parameters to the EBF3 process, i.e., by signaling a main process controller to change one or more of these parameters, to thereby control the EBF3 process in a closed-loop manner.
As discussed in the Taminger '410 patent publication, a sensor in the form of a side-view optical camera can be used to monitor the height of a deposited bead on a substrate, and the distance between the deposited bead and the wire feeder. In such an embodiment, cross-hairs may be superimposed over the optical image, with the z-height of the deposit adjusted up or down to maintain the height of the current deposited layer centered on the cross-hairs.
During known EBF3 processes, a human operator sets the height of the electron beam gun relative to the substrate. To initiate the start of a new layer the operator estimates visually where the wire should be in reference to the height of the previous deposit. If, because of a had estimation or a love spot in the previous layer, the feed height becomes too high, drips can result and the operator must input a command to lower the height of the electron beam gun and wire feeder. If the estimation is too low the feed wire can scrape against the previous deposit and can be forced out of the molten pool. In some cases, the misaligned wire can fuse with the previous deposit near the molten pool and cause a “wire stick.” In that case the deposition process must be halted so that the wire can be cut away from the deposition.